Field of the Invention
The present invention relates to a pneumatic tire.
More specifically, the present invention relates to a pneumatic tire including an inner liner layer formed as follows. A laminate sheet is obtained by laminating: a sheet made from a thermoplastic resin or a thermoplastic resin composition which is a blend of the thermoplastic resin and an elastomer; and a rubber to be bonded by curing to the thermoplastic resin or the thermoplastic resin composition. The laminate sheet is cut to a predetermined length. End portions of the laminate sheet are spliced together. The resultant product is cured and molded into the inner liner sheet. This pneumatic tire does not develop cracks around a splice portion of the spliced laminate sheet (inner liner layer) after the pneumatic tire starts to be used for driving, and accordingly has excellent durability.
Background Information
In recent years, proposals and studies have been made to use a sheet-shaped object, formed from a thermoplastic resin or a thermoplastic resin composition which is a blend of the thermoplastic resin and an elastomer, as an inner liner of a pneumatic tire Japanese patent application Kokai publication No. 2009-241855.
For actual use of the sheet-shaped object formed from the thermoplastic resin or the thermoplastic resin composition which is the blend of the thermoplastic resin and the elastomer as the inner liner for the pneumatic tire, the following manufacturing method is generally employed. A laminate sheet is formed which includes: a sheet made from a thermoplastic resin or a thermoplastic resin composition which is a blend of the thermoplastic resin and an elastomer; and a rubber (tie rubber) sheet to be bonded by curing to the thermoplastic resin or the thermoplastic resin which is the blend of the thermoplastic resin and the elastomer. The laminate sheet is wound around a tire building drum, and is subjected to lap-splicing. The resultant product is subsequently subjected to a curing and molding process.
However, there is a case where a tire is manufactured by: pulling out a predetermined length of the laminate sheet including the thermoplastic resin or the thermoplastic resin composition which is the blend of the thermoplastic resin and the elastomer and the tie rubber layer, which has been wound into a rolled shape, from its roll and cutting out the laminate sheet; winding the laminate sheet around the tire building drum; lap-splicing the laminate sheet on the drum; and further curing and molding the resultant product. In this case, the components constituting the inner liner, namely, the sheet made from the thermoplastic resin or the thermoplastic resin composition, and the tie rubber sheet bonded by curing to the sheet made from the thermoplastic resin or the plastic resin composition, may be detached from each other after the tire starts to be used for driving.
This situation will be explained with drawings. As shown in FIG. 2(a), a laminate sheet 1 including: a sheet 2 made from a thermoplastic resin or a thermoplastic resin composition which is a blend of the thermoplastic resin and an elastomer; and a tie rubber layer 3, is cut to a desired size (length) with an edged tool, for example. Then, on a tire building drum, two end portions of the laminate sheet 1 are spliced together, with a lap splice portion S defined at the two ends thereof, into a way that the laminate sheet 1 is formed into an annular shape. Incidentally, when one laminate sheet 1 is used, the laminate sheet 1 is formed into an annular shape by splicing its two end portions together. When multiple laminate sheets 1 are used, the laminate sheets 1 are formed into an annular shape by splicing their end portions to one another.
Thereafter, other parts (not illustrated) needed for manufacturing the tire are wound, and then a curing and molding process is performed with a bladder. After the curing and molding process, as shown in a model diagram of FIG. 2(b), an inner liner layer 10 is formed which includes: the sheet 2 made from the thermoplastic resin or the thermoplastic resin composition which is the blend of the thermoplastic resin and the elastomer; and the tie rubber layer 3. In the vicinity of the splice portion S, there are formed a portion where the sheet 2 made from the thermoplastic resin or the thermoplastic resin composition is exposed, and a portion where the sheet 2 is buried in the tie rubber layer.
The above-mentioned phenomenon of detachment between the sheet 2, which is made from the thermoplastic resin or the thermoplastic resin composition, and the tie rubber sheet 3 bonded by curing thereto occurs particularly in the vicinity 4 shown in FIG. 2(b), for example, of the exposed tip portion of the sheet 2 made from the thermoplastic resin composition . Here, a crack occurs in the beginning, and then develops into the sheet detachment phenomenon.